Asbestos Called a Cause of Laryngeal Cancer

Action Points

Explain to patients who ask that exposure to asbestos fibers, once widely used in insulation, has been shown to increase the risk of laryngeal cancer as well as lung cancer and mesothelioma.

WASHINGTON, June 9 â€” Asbestos â€” long associated with mesothelioma and lung cancer â€” also appears to be a cause of laryngeal malignancies, according to the Institute of Medicine.

In a new report, the IOM also concluded there is "suggestive but not sufficient" evidence to conclude the mineral fibers are a cause of pharyngeal, stomach, and colorectal cancer. The evidence is inadequate to allow any conclusions about the relationship between asbestos and esophageal cancer, said the IOM report.

The U.S. Senate sparked the analysis, commissioning the quasi-governmental institute, a component of the National Academy of Sciences, to "comprehensively review, evaluate, and summarize the peer-reviewed scientific and medical literature" on asbestos and the five forms of cancer. The need for the study arose during debate on legislation to create a $140 billion asbestos-injury compensation fund.

According to the American Cancer Society, there will be about 9,510 new cases of cancer of the larynx this year, and 3,740 deaths. The main risk factors for laryngeal cancer are smoking and heavy consumption of alcohol and the two factors are synergistic. One study found that heavy smokers and drinkers had a relative risk for laryngeal cancer of 22.1, compared with people who neither smoked nor drank.

The IOM's multidisciplinary research committee found 35 cohort studies and 15-case-control studies that evaluated the link between asbestos and cancer of the larynx.

The populations in the cohort studies were drawn from a wide range of industries, including mining, textiles, and insulation, the report said. Five studies looked at incidence of cancer in exposed and unexposed subjects, while the remainder studied mortality.

The number of deaths reported in the studies ranged from one to 36, but in all of the studies in which more than 10 deaths from cancer of the larynx were reported, the relative risk for cancer was greater than one for exposed persons, compared to those without exposure to asbestos.

Overall, the report concluded, the case-control studies indicated a relative risk for cancer in exposed persons of 1.40 (with a 95% confidence interval from 1.19 to 1.64), compared to non-exposed subjects.

In the 15 case-control studies, only one had a relative risk for cancer that was below one, although several had positive associations that failed to achieve significance. Nevertheless, the overall risk was very similar to that found in the cohort studies: Exposed persons had a relative risk of 1.43 for cancer, compared to non-exposed subjects. The 95% confidence interval ranged from 1.15 to 1.78.

The researchers also isolated the 10 studies considered to have the best information on exposure and calculated a combined relative risk in those analyses. The risk of cancer, they found, was lower, at 1.21 for exposed subjects, but still significant. The 95% confidence interval ranged from 1.04 to 1.40.

Many of the case-control studies tried to control for tobacco and alcohol use. After adjusting for those risk factors, the relative risk of cancer for an exposed person became 1.18, with a 95% confidence interval from 1.01 to 1.37.

The institute noted that the association is biologically plausible - the larynx, like the lung, lies anatomically in the direct path of inhaled asbestos fibers. Also:

Inflammation or damage to the vocal folds could disrupt the smooth flow of inhaled and exhaled air and allow asbestos fibers to build up in the larynx.

Squamous-cell carcinomas of the lung and larynx are both clinically and histologically similar.

Cancers at both sites arise from the respiratory epithelium.

Tobacco is the chief risk factor for cancer at both sites.

However, the report noted, there's no evidence that asbestos fibers accumulate and persist in the larynx. As well, there is a lack of experimental support from animal studies.

Reviewed by Zalman S. Agus, MD Emeritus Professor at the University of Pennsylvania School of Medicine

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